Isoprenoid pathway inhibitors for stimulating bone growth

ABSTRACT

Compounds of the formula                    
     wherein X in each of formulas (1) and (2) represents a substituted or unsubstituted alkylene, alkenylene, or alkynylene linker of 2-6C; 
     Y is of the formula                    
      or a stereoisomer thereof, 
     wherein R 1  is substituted or unsubstituted alkyl; 
     each R 2  is independently H, hydroxy, alkoxy (1-6C) or lower alkyl (1-4C); 
     R 3  is H, hydroxy, or alkoxy (1-6C); or 
     Y is of the formula                    
      wherein each n is 1, 
     Z is N, 
     K comprises a substituted or unsubstituted aromatic carbocyclic or heterocyclic ring system which may optionally be spaced from the linkage position shown in formula (7) by a linker of 1-2C, or in formula (7), Z may be spaced from the carbon bonded to X by ═CR 6 — wherein R 6  is H or linear, branded or cyclic alkyl (1-6C), 
     R 5  is H or linear, branched or cyclic alkyl, and 
     R′ represents a cation, H or a substituted or unsubstituted alkyl group of 1-6C, 
     promote bone formation and are thus useful in treating osteoporosis, bone fracture or deficiency, primary or secondary hyperparathyroidism, periodontal disease or defect, metastatic bone disease, osteolytic bone disease, post-plastic surgery, post-prosthetic joint surgery, and post-dental implantation. 
     Also disclosed is a method to identify additional compounds which are inhibitors of enzymes in the isoprenoid scheme especially of HMG-CoA reductase which results in prenylation of proteins and in the synthesis of steroids or of inhibitors of their production which are useful in treating bone disorders.

This application is a divisional of application Ser. No. 09/488,380 filed Jan. 20, 2000 now U.S. Pat. No. 6,376,476 claims priority under 35 U.S.C. §119 from provisional application Ser. No. 60/032,893 filed Dec. 13, 1996. It is also a continuation-in-part of U.S. Ser. No. 09/096,631 filed Jun. 12, 1998 abandoned which is a continuation-in-part of U.S. Ser. No. 08/989,862 filed Dec. 12, 1997 now U.S. Pat. No. 6,022,887 claiming benefit under 35 U.S.C. §120. The entire contents of these documents are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to screening methods for compositions and to methods to use these compositions in treating bone disorders in vertebrates including fractures and cartilage disorders. More specifically, the invention concerns a method to identify agents that will be useful in treating bone disorders by assessing their ability to inhibit enzymes in the isoprenoid synthesis pathway and in particular, to inhibit HMG-CoA reductase, and to methods and compositions useful in treating bone disorders which contain the identified active ingredients as essential components.

BACKGROUND ART

Bone is subject to constant breakdown and resynthesis in a complex process mediated by osteoblasts, which produce new bone, and osteoclasts, which destroy bone. The activities of these cells are regulated by a large number of cytokines and growth factors, many of which have now been identified and cloned.

There is a plethora of conditions which are characterized by the need to enhance bone formation. Perhaps the most obvious is the case of bone fractures, where it would be desirable to stimulate bone growth and to hasten and complete bone repair. Agents that enhance bone formation would also be useful in facial reconstruction procedures. Other bone deficit conditions include bone segmental defects, periodontal disease, metastatic bone disease, osteolytic bone disease and conditions where connective tissue repair would be beneficial, such as healing or regeneration of cartilage defects or injury. Also of great significance is the chronic condition of osteoporosis, including age-related osteoporosis and osteoporosis associated with post-menopausal hormone status. Other conditions characterized by the need for bone growth include primary and secondary hyperparathyroidism, disuse osteoporosis, diabetes-related osteoporosis, and glucocorticoid-related osteoporosis.

One group of compounds suggested for enhancing bone formation comprises bone morphogenic proteins (BMPs). The BMPs are novel factors in the extended transforming growth factor β superfamily. Recombinant BMP-2 and BMP-4 can induce new bone formation when they are injected locally into the subcutaneous tissues of rats (Wozney J. Molec Reprod Dev (1992) 32:160-67). These factors are expressed by normal osteoblasts as they differentiate, and have been shown to stimulate osteoblast differentiation and bone nodule formation in vitro as well as bone formation in vivo (Harris S., et al., J. Bone Miner Res (1994) 9:855-63). This latter property suggests potential usefulness as therapeutic agents in diseases which result in bone loss.

The cells which are responsible for forming bone are osteoblasts. As osteoblasts differentiate from precursors to mature bone-forming cells, they express and secrete a number of enzymes and structural proteins of the bone matrix, including Type-1 collagen, osteocalcin, osteopontin and alkaline phosphatase (Stein G., et al., Curr Opin Cell Biol (1990) 2:1018-27; Harris S., et al., (1994), supra). They also synthesize a number of growth regulatory peptides which are stored in the bone matrix, and are presumably responsible for normal bone formation. These growth regulatory peptides include the BMPs (Harris S., et al. (1994), supra). In studies of primary cultures of fetal rat calvarial osteoblasts, BMPs 1, 2, 3, 4, and 6 are expressed by cultured cells prior to the formation of mineralized bone nodules (Harris S., et al. (1994), supra). Like alkaline phosphatase, osteocalcin and osteopontin, the BMPs are expressed by cultured osteoblasts as they proliferate and differentiate.

Although the BMPs are potent stimulators of bone formation in vitro and in vivo, there are disadvantages to their use as therapeutic agents to enhance bone healing. Receptors for the bone morphogenetic proteins have been identified in many tissues, and the BMPs themselves are expressed in a large variety of tissues in specific temporal and spatial patterns. This suggests that BMPs may have effects on many tissues in addition to bone, potentially limiting their usefulness as therapeutic agents when administered systemically. Moreover, since they are peptides, they would have to be administered by injection. These disadvantages impose severe limitations to the development of BMPs as therapeutic agents.

Small molecules that are useful in treating bone disorders in vertebrates are of the general formula Ar¹-L-Ar² wherein Ar¹ and Ar² are aromatic moieties and L is a linker that separates them by a specified distance. These are disclosed in PCT application WO98/17267 published Apr. 30, 1998. These compounds were assessed for usefulness in treating bone disorders by their ability to enhance the production of a reporter protein when the nucleotide sequence encoding the reporter protein is operably linked to the promoter for BMP-2. Similar compounds are disclosed for this purpose in earlier filed PCT applications WO97/15308 published May 1, 1997 and WO97/48694 published Dec. 24, 1997. The present application concerns another class of compounds that are inhibitors of β-hydroxy-β-methyl glutaric acid CoA (HMG-CoA) reductase that are also successful in this assay. The compounds described in the present application are generically known as “statins.”

Statins are HMG-CoA reductase inhibitors (Bilheimer, D. W., Drug Investigation (1900) 2 (Suppl. 2) 58-67). HMG-CoA reductase is the principal rate limiting enzyme involved in cellular cholesterol biosynthesis. The pathway is also responsible for the production of dolichol, ubiquinones, isopentenyl adenine and farnesol. HMG-CoA reductase converts 3-hydroxy-3-methyl-glutaryl CoA (HMG-CoA) to mevalonate. Addition of mevalonate at concentrations between 25-800 μM inhibits the activity of mevastatin (100, 25, or 6.25 μM) in the ABA assay described in Example 1 herein. Mevalonic acid has no effect on primary screen activities of bone growth-active compounds outside of the statin family (compounds 59-0008 (see Example 1)). These data indicate that the effect of mevastatin in the ABA assay is mediated by its effect on HMG-CoA reductase. Knowledge of inhibitors of the cholesterol biosynthetic pathway (including SAR or pharmacophore analyses) may be useful in determining appropriate modifications or analogs of the statins that maintain bone growth activity.

U.S. Pat. No. 5,280,040 discloses compounds described as useful in the treatment of osteoporosis. These compounds putatively achieve this result by preventing bone resorption. Related to these compounds are the bisphosphonates—the methylene bisphosphonic acids. These compounds are comprised of two phosphonic acid residues coupled through a methylene linkage. Typical representatives include the clodronates which are simple compounds wherein the phosphonic acid residues are coupled through dichloromethylene. Other representative bisphosphonates include ibandronates, the risedronates, alandronates and pamidronates. These compounds have been shown to inhibit the resorption of bone, presumably by effecting apoptosis of osteoclasts. Luckman, S. P., et al., J Bone Min Res (1998) 13:581-589.

Wang, G.-J., et al., J Formos Med Assoc (1995) 94:589-592 report that certain lipid clearing agents, exemplified by lovastatin and bezafibrate, were able to inhibit the bone resorption resulting from steroid administration in rabbits. There was no effect on bone formation by these two compounds in the absence of steroid treatment. The mechanism of the inhibition in bone resorption observed in the presence of steroids (and the mechanism of the effect of steroid on bone per se) is said to be unknown. The authors state that steroid-induced bone loss is associated with a decrease in bone formation attributed to an inhibitory effect of corticosteroid on osteoblast activity and an increase in bone absorption due to direct osteoclast stimulation and to an indirect inhibition of intestinal calcium absorption with a secondary increase in parathyroid hormone production. Other mechanisms mentioned include those attributable to lipid abnormalities and hyperlipidemia which lead to circulatory impairment, obstruction of subchondral vessels, osteocyte necrosis and osteoporosis. In light of the known activities of lovastatin and bezafibrate, the authors attribute the effect on bone loss to their ability to lower lipid levels and overcome the impairment to circulation within the femoral head. There is no suggestion in Wang, et al., that lovastatin directly enhances bone formation.

An abstract entitled “Lovastatin Prevents Steroid-Induced Adipogenesis and Osteoporosis” by Cui, Q., et al., appeared in the Reports of the ASBMR 18th Annual Meeting (September 1996) J. Bone Mineral Res. (1996) 11(S1):S510. The abstract reports that lovastatin diminished triglyceride vesicles that accumulated when osteoprogenitor cells cloned from bone marrow stroma of chickens were treated in culture with dexamethasone. Lovastatin was reported to diminish the expression of certain mRNAs and to allow the cells to maintain the osteogenic phenotype after dexamethasone treatment. Further, chickens that had undergone bone loss in the femoral head as a result of dexamethasone treatment were improved by treatment with lovastatin. Again, there is no suggestion that lovastatin directly enhances bone formation in the absence of steroid treatment.

In any event, these data are contrary to reports that dexamethasone and other inducers, such as BMPs, induce osteoblastic differentiation and stimulate osteocalcin mRNA (Bellows, C. G., et al., Develop Biol (1990) 140:132-38; Rickard, D. J., et al., Develop Biol (1994) 161:218-28). In addition, Ducy, P., et al., Nature (1996) 382:448-52 have recently reported that osteocalcin deficient mice exhibit a phenotype marked by increased bone formation and bones of improved functional quality, without impairment of bone resorption. Ducy, et al., state that their data suggest that osteocalcin antagonists may be of therapeutic use in conjunction with estrogen replacement therapy (for prevention or treatment of osteoporosis).

The present invention discloses not only the class of compounds generally called the “statins” for use in stimulating bone formation, but also provides a method to identify compounds useful in this regard by assessing their ability to inhibit enzymes in the pathway of isoprenoid synthesis. These enzymes include HMG-CoA reductase (inhibited by the statins), and also the enzymes responsible for production of the geranyl and farnesyl intermediates on the pathway to the synthesis of squalene and ultimately the steroids and the enzymes which catalyze the addition of farnesyl units or geranyl-geranyl units to proteins.

DISCLOSURE OF THE INVENTION

In one aspect, the invention provides statin-type compounds that can be administered as ordinary pharmaceuticals and have the metabolic effect of directly enhancing bone growth. The statins can be confirmed in this property using an assay for their ability to activate control elements associated with endogenous factors that stimulate bone growth. Thus, the invention is directed to methods and compositions for stimulating the growth of skeletal (bone) tissue, which methods and compositions use, as at least one of the active ingredients, compounds which are characterized as “statins” by virtue of their ability to inhibit HMG-CoA reductase. Typical statins are of the formula:

wherein X in each of formulas (1) and (2) represents a substituted or unsubstituted alkylene, alkenylene, or alkynylene linker of 2-6C;

Y represents one or more carbocyclic or heterocyclic rings; when two or more rings are present in Y, they may optionally be fused; and

R′ represents a cation, H or a substituted or unsubstituted alkyl group of 1-6C.

Thus, the invention is directed to methods to treat bone disorders by directly stimulating bone formation using the statins described and to pharmaceutical compositions for this use.

In still another aspect, the invention is directed to methods to identify additional compounds which are useful in methods to treat bone disorders by assessing their ability to inhibit enzymes significant in the isoprenoid synthesis pathway, especially HMG-CoA reductase, but also including subsequent steps resulting in the synthesis of steroids and subsequent steps resulting in the prenylation of proteins. Compounds identified in this manner can be confirmed as useful in treating bone disorders in any of a number of assays described hereinbelow. The invention is also directed to methods to treat bone disorders using compounds that are inhibitors of the isoprenoid and isoprenoid-related pathways.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show the structures and activity of several compounds of the invention in the ABA screening assay of Example 1.

FIG. 2 shows an outline of the synthesis pathway for isoprenoids and the pathways of their subsequent conversion to squalene and steroids and in prenylating target proteins.

MODES OF CARRYING OUT THE INVENTION

The ultimate goal of the methods and compositions of the invention is to treat or ameliorate bone disorders in vertebrate subjects, particularly mammals, and more particularly humans.

As used herein, “treat” or “treatment” include a postponement of development of bone deficit symptoms and/or a reduction in the severity of such symptoms that will or are expected to develop. The terms further include ameliorating existing bone or cartilage deficit symptoms, preventing additional symptoms, ameliorating or preventing the underlying metabolic causes of symptoms, preventing or reversing bone resorption and/or encouraging bone growth. Thus, the terms denote that a beneficial result has been conferred on a vertebrate subject with a cartilage, bone or skeletal deficit, or with the potential to develop such deficit.

By “bone deficit” is meant an imbalance in the ratio of bone formation to bone resorption, such that, if unmodified, the subject will exhibit less bone than desirable, or the subject's bones will be less intact and coherent than desired. Bone deficit may also result from fracture, from surgical intervention or from dental or periodontal disease. By “cartilage defect” is meant damaged cartilage, less cartilage than desired, or cartilage that is less intact and coherent than desired. “Bone disorders” includes both bone deficits and cartilage defects.

Representative uses of the compounds of the present invention include: repair of bone defects and deficiencies, such as those occurring in closed, open and non-union fractures; prophylactic use in closed and open fracture reduction; promotion of bone healing in plastic surgery; stimulation of bone ingrowth into non-cemented prosthetic joints and dental implants; elevation of peak bone mass in pre-menopausal women; treatment of growth deficiencies; treatment of periodontal disease and defects, and other tooth repair processes; increase in bone formation during distraction osteogenesis; and treatment of other skeletal disorders, such as age-related osteoporosis, post-menopausal osteoporosis, glucocorticoid-induced osteoporosis or disuse osteoporosis and arthritis, or any condition that benefits from stimulation of bone formation. The compounds of the present invention can also be useful in repair of congenital, trauma-induced or surgical resection of bone (for instance, for cancer treatment), and in cosmetic surgery. Further, the compounds of the present invention can be used for limiting or treating cartilage defects or disorders, and may be useful in wound healing or tissue repair.

Bone or cartilage deficit or defect can be treated in vertebrate subjects by administering compounds of the invention which exhibit certain structural and functional characteristics. The compositions of the invention may be administered systemically or locally. For systemic use, the compounds herein are formulated for parenteral (e.g., intravenous, subcutaneous, intramuscular, intraperitoneal, intranasal or transdermal) or enteral (e.g., oral or rectal) delivery according to conventional methods. Intravenous administration can be by a series of injections or by continuous infusion over an extended period. Administration by injection or other routes of discretely spaced administration can be performed at intervals ranging from weekly to once to three times daily. Alternatively, the compounds disclosed herein may be administered in a cyclical manner (administration of disclosed compound; followed by no administration; followed by administration of disclosed compound, and the like). Treatment will continue until the desired outcome is achieved. In general, pharmaceutical formulations will include a compound of the present invention in combination with a pharmaceutically acceptable vehicle, such as saline, buffered saline, 5% dextrose in water, borate-buffered saline containing trace metals or the like. Formulations may further include one or more excipients, preservatives, solubilizers, buffering agents, albumin to prevent protein loss on vial surfaces, lubricants, fillers, stabilizers, etc. Methods of formulation are well known in the art and are disclosed, for example, in Remington's Pharmaceutical Sciences, latest edition, Mack Publishing Co., Easton Pa., which is incorporated herein by reference. Pharmaceutical compositions for use within the present invention can be in the form of sterile, non-pyrogenic liquid solutions or suspensions, coated capsules, suppositories, lyophilized powders, transdermal patches or other forms known in the art. Local administration may be by injection at the site of injury or defect, or by insertion or attachment of a solid carrier at the site, or by direct, topical application of a viscous liquid, or the like. For local administration, the delivery vehicle preferably provides a matrix for the growing bone or cartilage, and more preferably is a vehicle that can be absorbed by the subject without adverse effects.

Delivery of compounds herein to wound sites may be enhanced by the use of controlled-release compositions, such as those described in PCT application WO 93/20859, which is incorporated herein by reference. Films of this type are particularly useful as coatings for prosthetic devices and surgical implants. The films may, for example, be wrapped around the outer surfaces of surgical screws, rods, pins, plates and the like. Implantable devices of this type are routinely used in orthopedic surgery. The films can also be used to coat bone filling materials, such as hydroxyapatite blocks, demineralized bone matrix plugs, collagen matrices and the like. In general, a film or device as described herein is applied to the bone at the fracture site. Application is generally by implantation into the bone or attachment to the surface using standard surgical procedures.

In addition to the copolymers and carriers noted above, the biodegradable films and matrices may include other active or inert components. Of particular interest are those agents that promote tissue growth or infiltration, such as growth factors. Exemplary growth factors for this purpose include epidermal growth factor (EGF), fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), transforming growth factors (TGFs), parathyroid hormone (PTH), leukemia inhibitory factor (LIF), insulin-like growth factors (IGFs) and the like. Agents that promote bone growth, such as bone morphogenetic proteins (U.S. Pat. No. 4,761,471; PCT Publication WO 90/11366), osteogenin (Sampath, et al., Proc. Natl. Acad. Sci. USA (1987) 84:7109-13) and NaF (Tencer, et al., J. Biomed. Mat. Res. (1989) 23: 571-89) are also contemplated. Biodegradable films or matrices include calcium sulfate, tricalcium phosphate, hydroxyapatite, polylactic acid, polyanhydrides, bone or dermal collagen, pure proteins, extracellular matrix components and the like and combinations thereof. Such biodegradable materials may be used in combination with non-biodegradable materials, to provide desired mechanical, cosmetic or tissue or matrix interface properties.

Alternative methods for delivery of compounds of the present invention include use of ALZET osmotic minipumps (Alza Corp., Palo Alto, Calif.); sustained release matrix materials such as those disclosed in Wang, et al. (PCT Publication WO 90/11366); electrically charged dextran beads, as disclosed in Bao, et al., (PCT Publication WO 92/03125); collagen-based delivery systems, for example, as disclosed in Ksander, et al., Ann. Surg. (1990) 211(3):288-94; methylcellulose gel systems, as disclosed in Beck, et al., J. Bone Min. Res. (1991) 6(11):1257-65; alginate-based systems, as disclosed in Edelman, et al., Biomaterials (1991) 12:619-26 and the like. Other methods well known in the art for sustained local delivery in bone include porous coated metal prostheses that can be impregnated and solid plastic rods with therapeutic compositions incorporated within them.

The compounds of the present invention may also be used in conjunction with agents that inhibit bone resorption. Antiresorptive agents, such as estrogen, bisphosphonates and calcitonin, are preferred for this purpose. More specifically, the compounds disclosed herein may be administered for a period of time (for instance, months to years) sufficient to obtain correction of a bone deficit condition. Once the bone deficit condition has been corrected, the vertebrate can be administered an anti-resorptive compound to maintain the corrected bone condition. Alternatively, the compounds disclosed herein may be administered with an anti-resorptive compound in a cyclical manner (administration of disclosed compound, followed by anti-resorptive, followed by disclosed compound, and the like).

In additional formulations, conventional preparations such as those described below may be used.

Aqueous suspensions may contain the active ingredient in admixture with pharmacologically acceptable excipients, comprising suspending agents, such as methyl cellulose; and wetting agents, such as lecithin, lysolecithin or long-chain fatty alcohols. The said aqueous suspensions may also contain preservatives, coloring agents, flavoring agents, sweetening agents and the like in accordance with industry standards.

Preparations for topical and local application comprise aerosol sprays, lotions, gels and ointments in pharmaceutically appropriate vehicles which may comprise lower aliphatic alcohols, polyglycols such as glycerol, polyethylene glycol, esters of fatty acids, oils and fats, and silicones. The preparations may further comprise antioxidants, such as ascorbic acid or tocopherol, and preservatives, such as p-hydroxybenzoic acid esters.

Parenteral preparations comprise particularly sterile or sterilized products. Injectable compositions may be provided containing the active compound and any of the well known injectable carriers. These may contain salts for regulating the osmotic pressure.

If desired, the osteogenic agents can be incorporated into liposomes by any of the reported methods of preparing liposomes for use in treating various pathogenic conditions. The present compositions may utilize the compounds noted above incorporated in liposomes in order to direct these compounds to macrophages, monocytes, as well as other cells and tissues and organs which take up the liposomal composition. The liposome-incorporated compounds of the invention can be utilized by parenteral administration, to allow for the efficacious use of lower doses of the compounds. Ligands may also be incorporated to further focus the specificity of the liposomes.

Suitable conventional methods of liposome preparation include, but are not limited to, those disclosed by Bangham, A. D., et al., J Mol Biol (1965) 23:238-252, Olson, F., et al., Biochim Biophys Acta (1979) 557:9-23, Szoka, F., et al., Proc Natl Acad Sci USA (1978) 75:4194-4198, Kim, S., et al., Biochim Biophys Acta (1983) 728:339:348, and Mayer, et al., Biochim Biophys Acta (1986) 858:161-168.

The liposomes may be made from the present compounds in combination with any of the conventional synthetic or natural phospholipid liposome materials including phospholipids from natural sources such as egg, plant or animal sources such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, sphingomyelin, phosphatidylserine, or phosphatidylinositol and the like. Synthetic phospholipids that may also be used, include, but are not limited to: dimyristoylphosphatidylcholine, dioleoylphosphatidylcholine, dipalmitoylphosphatidylcholine and distearoylphosphatidycholine, and the corresponding synthetic phosphatidylethanolamines and phosphatidylglycerols. Cholesterol or other sterols, cholesterol hemisuccinate, glycolipids, cerebrosides, fatty acids, gangliosides, sphingolipids, 1,2-bis(oleoyloxy)-3-(trimethyl ammonio) propane (DOTAP), N-[1-(2,3-dioleoyl) propyl-N,N,N-trimethylammonium chloride (DOTMA), and other cationic lipids may be incorporated into the liposomes, as is known to those skilled in the art. The relative amounts of phospholipid and additives used in the liposomes may be varied if desired. The preferred ranges are from about 60 to 90 mole percent of the phospholipid; cholesterol, cholesterol hemisuccinate, fatty acids or cationic lipids may be used in amounts ranging from 0 to 50 mole percent. The amounts of the present compounds incorporated into the lipid layer of liposomes can be varied with the concentration of the lipids ranging from about 0.01 to about 50 mole percent.

The liposomes with the above formulations may be made still more specific for their intended targets with the incorporation of monoclonal antibodies or other ligands specific for a target. For example, monoclonal antibodies to the BMP receptor may be incorporated into the liposome by linkage to phosphatidylethanolamine (PE) incorporated into the liposome by the method of Leserman, L., et al., Nature (1980) 288:602-604.

Veterinary uses of the disclosed compounds are also contemplated. Such uses would include treatment of bone or cartilage deficits or defects, i.e., bone disorders, in domestic animals, livestock and thoroughbred horses.

The compounds of the present invention may be used to stimulate growth of bone-forming cells or their precursors, or to induce differentiation of bone-forming cell precursors, either in vitro or ex vivo. The compounds described herein may also modify a target tissue or organ environment, so as to attract bone-forming cells to an environment in need of such cells. As used herein, the term “precursor cell” refers to a cell that is committed to a differentiation pathway, but that generally does not express markers or function as a mature, fully differentiated cell. As used herein, the term “mesenchymal cells” or “mesenchymal stem cells” refers to pluripotent progenitor cells that are capable of dividing many times, and whose progeny will give rise to skeletal tissues, including cartilage, bone, tendon, ligament, marrow stroma and connective tissue (see A. Caplan, J. Orthop. Res. (1991) 9:641-50). As used herein, the term “osteogenic cells” includes osteoblasts and osteoblast precursor cells. More particularly, the disclosed compounds are useful for stimulating a cell population containing marrow mesenchymal cells, thereby increasing the number of osteogenic cells in that cell population. In a preferred method, hematopoietic cells are removed from the cell population, either before or after stimulation with the disclosed compounds. Through practice of such methods, osteogenic cells may be expanded. The expanded osteogenic cells can be infused (or reinfused) into a vertebrate subject in need thereof. For instance, a subject's own mesenchymal stem cells can be exposed to compounds of the present invention ex vivo, and the resultant osteogenic cells could be infused or directed to a desired site within the subject, where further proliferation and/or differentiation of the osteogenic cells can occur without immunorejection. Alternatively, the cell population exposed to the disclosed compounds may be immortalized human fetal osteoblastic or osteogenic cells. If such cells are infused or implanted in a vertebrate subject, it may be advantageous to “immunoprotect” these non-self cells, or to immunosuppress (preferably locally) the recipient to enhance transplantation and bone or cartilage repair.

Within the present invention, an “effective amount” of a composition is that amount which produces a statistically significant effect. For example, an “effective amount” for therapeutic uses is the amount of the composition comprising an active compound herein required to provide a clinically significant increase in healing rates in fracture repair; reversal of bone loss in osteoporosis; reversal of cartilage defects or disorders; prevention or delay of onset of osteoporosis; stimulation and/or augmentation of bone formation in fracture non-unions and distraction osteogenesis; increase and/or acceleration of bone growth into prosthetic devices; and repair of dental defects. Such effective amounts will be determined using routine optimization techniques and are dependent on the particular condition to be treated, the condition of the patient, the route of administration, the formulation, and the judgment of the practitioner and other factors evident to those skilled in the art. The dosage required for the compounds of the invention (for example, in osteoporosis where an increase in bone formation is desired) is manifested as a statistically significant difference in bone mass between treatment and control groups. This difference in bone mass may be seen, for example, as a 5-20% or more increase in bone mass in the treatment group. Other measurements of clinically significant increases in healing may include, for example, tests for breaking strength and tension, breaking strength and torsion, 4-point bending, increased connectivity in bone biopsies and other biomechanical tests well known to those skilled in the art. General guidance for treatment regimens is obtained from experiments carried out in animal models of the disease of interest.

The dosage of the compounds of the invention will vary according to the extent and severity of the need for treatment, the activity of the administered compound, the general health of the subject, and other considerations well known to the skilled artisan. Generally, they can be administered to a typical human on a daily basis as an oral dose of about 0.1 mg/kg-1000 mg/kg, and more preferably from about 1 mg/kg to about 200 mg/kg. The parenteral dose will appropriately be 20-100% of the oral dose. While oral administration may be preferable in most instances (for reasons of ease, patient acceptability, and the like), alternative methods of administration may be appropriate for selected compounds and selected defects or diseases. In comparative assays, positive control compounds or other bone-active test compounds may be administered subcutaneously, while statin-type test compounds are administered orally.

Identification of Statins and Other Isoprenoid Pathway Inhibitors

The compounds of the invention which are useful in treating bone disorders by enhancing bone growth are generally classified as “statins.” Statins are known to inhibit the enzyme HMG-CoA reductase. The structure of a number of statins, currently used as drugs to inhibit cholesterol formation, are shown in FIG. 1. Members of this group of compounds have found considerable practical application and are marketed as cholesterol-lowering drugs. These include cerivastatin, marketed under the name Baycol® by Bayer (See U.S. Pat. Nos. 5,006,530 and 5,177,080), lovastatin, marketed under the name Mevacor® by Merck (See U.S. Pat. No. 4,963,538), and simvastatin, marketed under the name of Zocar®, pravastatin, marketed under the brand name Pravachol®, atorvastatin, marketed under the name Lipotor® by Warner-Lambert (See U.S. Pat. No. 5,273,995), and fluvastatin, marketed under the name Lescolo (See U.S. Pat. No. 4,739,073). Another known statin is NK-104 developed by NEGMA. (See Akiba, T et al., J Toxicol Sci (1998) 23V:713-720.) All the above-cited documents are incorporated herein by reference. In general, additional compounds of similar structure which are successful in inhibiting HMG-CoA reductase can be identified by standard assays well known in the art, and as described below.

FIG. 2 is a diagram of the synthetic pathway which includes isoprenoid intermediates and ultimately results in the formation of steroids or the prenylation of proteins. As used herein, “isoprenoid pathway” refers to the conversions summarized in this figure, and “enzymes of the isoprenoid pathway” refers to any enzyme which catalyzes these conversions. More detailed descriptions of the individual conversions in the general outline shown in FIG. 2 will be found in standard texts on metabolism and biochemistry. The outline in FIG. 2 is intended as an overview only, and does not depict each and every conversion step. These are as have been elucidated over the past 40 or so years in the study of acetate metabolism. Compounds which inhibit these pathways, represented by the diagram in FIG. 2, are also useful in stimulating bone growth or inhibiting bone resorption or both. Compounds that inhibit the various steps in this pathway can easily be identified by assessing their ability to inhibit the particular enzymes that catalyze the relevant steps. Thus, the invention is also directed to a method to identify compounds useful in the treatment of bone disorders which method comprises determining the ability of a candidate compound to inhibit an enzymic conversion in this pathway. This assay can be conducted by contacting said compound with an assay mixture for the activity of an enzyme in the isoprenoid pathway; determining the activity of the enzyme in the presence as compared to the absence of said compound; wherein a decrease of activity of said enzyme in the presence as opposed to the absence of said compound indicates that the compound will be useful in treating bone disorders in vertebrates.

Since the enzymes involved in this pathway are known and often commercially available, simple in vitro assays for this inhibition activity are well within ordinary skill.

In one aspect, the inhibition of the pathway diagrammed in FIG. 2 may result in the stimulation of bone formation by preventing prenylation of proteins which are inhibitory to the synthesis of bone when in their prenylated form. For example, the function of the ras protein is dependent on prenylation, and inhibition of the functions of ras protein in bone cells leads to increased bone formation as set forth in Example 7 below.

Compounds that are identified by their ability to inhibit the various enzymes in the isoprenoid synthesis pathway can be confirmed to stimulate bone formation by the use of suitable more direct assays as set forth hereinabove.

In addition, compounds useful in treating bone disorders can be identified by their ability to diminish the production of these enzymes. This can be assessed by testing the effect of a candidate compound on expression of a reporter gene under control of the expression control sequences for these enzymes. Assays for the ability of compounds to inhibit control sequences which control the production of, for example, HMG-CoA reductase are set forth in Yagi, Y., et al., Drug Development Research (1997) 40:41-47.

In general, the assays are conducted by contacting a candidate compound with an expression system wherein said expression system comprises a control sequence associated with an enzyme in the isoprenoid synthesis pathway operably linked to a reporter gene; comparing the expression of the reporter gene in the presence and absence of the compound; wherein a decrease in the expression of the reporter gene in the presence as compared to the absence of the compound indicates the compound will be useful in treating bone disorders in vertebrates.

In summary, the statins, known to be inhibitors of HMG-CoA reductase, presumably the rate-limiting step in the isoprenoid pathway, have been shown herein to directly stimulate the formation of bone. The bisphosphonates, which were shown by Luckman, S. P., et al., J Bone Min Res (1998) (supra) to inhibit prenylation of proteins, and other aminobisphosphonates which have been shown to inhibit squalene synthase (Aminn, et al., J Lipid Res (1992) 33:1657) have been shown herein to stimulate bone formation directly. Inhibition of the prenylation of ras protein has also been shown to be related to bone stimulation. Thus, generally, inhibitors of the isoprenoid pathway diagrammed in FIG. 2 including, especially, the statins and bisphosphonates, are useful in direct stimulation of bone formation.

Confirmatory Assays

The osteogenic activity of the compounds used in the methods of the invention which are identified by their effects on isoprenoid systems, especially HMG-CoA reductase, can be verified using in vitro screening techniques, such as the assessment of transcription of a reporter gene coupled to a bone morphogenetic protein-associated promoter or in alternative assays.

High Throughput Assay

A rapid throughput screening test for compounds that stimulate bone formation by demonstration that they are capable of stimulating expression of a reporter gene linked to a BMP promoter (a surrogate for the production of bone morphogenetic factors that are endogenously produced) is described in U.S. application Ser. No. 08/458,434, filed Jun. 2, 1995, and now allowed, the entire contents of which are incorporated herein by reference. This assay is also described as a portion of a study of immortalized murine osteoblasts (derived from a mouse expressing a transgene composed of a BMP-2 promoter driving expression of T-antigen) in Ghosh-Choudhery, N., et al., Endocrinology (1996) 137:331-39. In this study, the immortalized cells were stably transfected with a plasmid containing a luciferase reporter gene driven by a mouse BMP-2 promoter (−2736/114 bp), and responded in a dose-dependent manner to recombinant human BMP-2.

Briefly, the assay utilizes cells transformed permanently or transiently with constructs in which the promoter of a bone morphogenetic protein, specifically BMP-2 or BMP-4, is coupled to a reporter gene, typically luciferase. These transformed cells are then evaluated for the production of the reporter gene product; compounds that activate the BMP promoter will drive production of the reporter protein, which can be readily assayed. Many thousands of compounds have been subjected to this rapid screening technique, and only a very small percentage are able to elicit a level of expression of reporter gene 5-fold greater than that produced by vehicle. Compounds that activate the BMP promoter fall into groups, where members of each group share certain structural characteristics not present in inactive compounds. The active compounds (“BMP promoter-active compounds” or “active compounds”) are useful in promoting bone or cartilage growth, and thus in the treatment of vertebrates in need of bone or cartilage growth.

BMP promoter-active compounds can be examined in a variety of other assays that test specificity and toxicity. For instance, non-BMP promoters or response elements can be linked to a reporter gene and inserted into an appropriate host cell. Cytotoxicity can be determined by visual or microscopic examination of BMP promoter- and/or non-BMP promoter-reporter gene-containing cells, for instance. Alternatively, nucleic acid and/or protein synthesis by the cells can be monitored. For in vivo assays, tissues may be removed and examined visually or microscopically, and optionally examined in conjunction with dyes or stains that facilitate histologic examination. In assessing in vivo assay results, it may also be useful to examine biodistribution of the test compound, using conventional medicinal chemistry/animal model techniques.

Neonatal Mouse Calvaria Assay (In vitro)

An assay for bone resorption or bone formation is similar to that described by Gowen M. & Mundy G., J Immunol (1986) 136:2478-82. Briefly, four days after birth, the front and parietal bones of ICR Swiss white mouse pups are removed by microdissection and split along the sagittal suture. In an assay for resorption, the bones are incubated in BGJb medium (Irvine Scientific, Santa Ana, Calif.) plus 0.02% (or lower concentration) β-methylcyclodextrin, wherein the medium also contains test or control substances. The medium used when the assay is conducted to assess bone formation is Fitton and Jackson Modified BGJ Medium (Sigma) supplemented with 6 μg/ml insulin, 6 μg/ml transferrin, 6 ng/ml selenous acid, calcium and phosphate concentrations of 1.25 and 3.0 mM, respectively, and ascorbic acid to a concentration of 100 μg/ml is added every two days. The incubation is conducted at 37° C. in a humidified atmosphere of 5% CO₂ and 95% air for 96 hours.

Following this, the bones are removed from the incubation media and fixed in 10% buffered formalin for 24-48 hours, decalcified in 14% EDTA for 1 week, processed through graded alcohols; and embedded in paraffin wax. Three μm sections of the calvaria are prepared. Representative sections are selected for histomorphometric assessment of bone formation or bone resorption. Bone changes are measured on sections cut 200 μm apart. Osteoblasts and osteoclasts are identified by their distinctive morphology.

Other auxiliary assays can be used as controls to determine non-BMP promoter-mediated effects of test compounds. For example, mitogenic activity can be measured using screening assays featuring a serum-response element (SRE) as a promoter and a luciferase reporter gene. More specifically, these screening assays can detect signaling through SRE-mediated pathways, such as the protein kinase C pathway. For instance, an osteoblast activator SRE-luciferase screen and an insulin mimetic SRE-luciferase screen are useful for this purpose. Similarly, test compound stimulation of cAMP response element (CRE)-mediated pathways can also be assayed. For instance, cells transfected with receptors for PTH and calcitonin (two bone-active agents) can be used in CRE-luciferase screens to detect elevated cAMP levels. Thus, the BMP promoter specificity of a test compound can be examined through use of these types of auxiliary assays.

In vivo Assay of Effects of Compounds on Murine Calvarial Bone Growth

Male ICR Swiss white mice, aged 4-6 weeks and weighing 13-26 gm, are employed, using 4-5 mice per group. The calvarial bone growth assay is performed as described in PCT application WO 95/24211, incorporated by reference. Briefly, the test compound or appropriate control vehicle is injected into the subcutaneous tissue over the right calvaria of normal mice. Typically, the control vehicle is the vehicle in which the compound was solubilized, and is PBS containing 5% DMSO or is PBS containing Tween (2 μl/10 ml). The animals are sacrificed on day 14 and bone growth measured by histomorphometry. Bone samples for quantitation are cleaned from adjacent tissues and fixed in 10% buffered formalin for 24-48 hours, decalcified in 14% EDTA for 1-3 weeks, processed through graded alcohols; and embedded in paraffin wax. Three to five μm sections of the calvaria are prepared, and representative sections are selected for histomorphometric assessment of the effects on bone formation and bone resorption. Sections are measured by using a camera lucida attachment to trace directly the microscopic image onto a digitizing plate. Bone changes are measured on sections cut 200 μm apart, over 4 adjacent 1×1 mm fields on both the injected and noninjected sides of the calvaria. New bone is identified by its characteristic woven structure, and osteoclasts and osteoblasts are identified by their distinctive morphology. Histomorphometry software (OsteoMeasure, Osteometrix, Inc., Atlanta) is used to process digitizer input to determine cell counts and measure areas or perimeters.

Additional In Vivo Assays

Lead compounds can be further tested in intact animals using an in vivo, dosing assay. Prototypical dosing may be accomplished by subcutaneous, intraperitoneal or oral administration, and may be performed by injection, sustained release or other delivery techniques. The time period for administration of test compound may vary (for instance, 28 days as well as 35 days may be appropriate). An exemplary, in vivo oral or subcutaneous dosing assay may be conducted as follows:

In a typical study, 70 three-month-old female Sprague-Dawley rats are weight-matched and divided into seven groups, with ten animals in each group. This includes a baseline control group of animals sacrificed at the initiation of the study; a control group administered vehicle only; a PBS-treated control group; and a positive control group administered a compound (non-protein or protein) known to promote bone growth. Three dosage levels of the compound to be tested are administered to the remaining three groups.

Briefly, test compound, positive control compound, PBS, or vehicle alone is administered subcutaneously once per day for 35 days. All animals are injected with calcein nine days and two days before sacrifice (two injections of calcein administered each designated day). Weekly body weights are determined. At the end of the 35-day cycle, the animals are weighed and bled by orbital or cardiac puncture. Serum calcium, phosphate, osteocalcin, and CBCs are determined. Both leg bones (femur and tibia) and lumbar vertebrae are removed, cleaned of adhering soft tissue, and stored in 70% ethanol for evaluation, as performed by peripheral quantitative computed tomography (pQCT; Ferretti, J., Bone (1995) 17:353S-64S), dual energy X-ray absorptiometry (DEXA; Laval-Jeantet A., et al., Calcif Tissue Intl (1995) 56:14-18; J. Casez, et al., Bone and Mineral (1994) 26:61-68) and/or histomorphometry. The effect of test compounds on bone remodeling can thus be evaluated.

Lead compounds can also be tested in acute ovariectomized animals (prevention model) using an in vivo dosing assay. Such assays may also include an estrogen-treated group as a control. An exemplary subcutaneous dosing assay is performed as follows:

In a typical study, 80 three-month-old female Sprague-Dawley rats are weight-matched and divided into eight groups, with ten animals in each group. This includes a baseline control group of animals sacrificed at the initiation of the study; three control groups (sham ovariectomized (sham OVX)+vehicle only; ovariectomized (OVX)+vehicle only; PBS-treated OVX); and a control OVX group that is administered a compound known to promote bone growth. Three dosage levels of the compound to be tested are administered to the remaining three groups of OVX animals.

Since ovariectomy (OVX) induces hyperphagia, all OVX animals are pair-fed with sham OVX animals throughout the 35 day study. Briefly, test compound, positive control compound, PBS, or vehicle alone is administered orally or subcutaneously once per day for 35 days. Alternatively, test compound can be formulated in implantable pellets that are implanted for 35 days, or may be administered orally, such as by gastric gavage. All animals, including sham OVX/vehicle and OVX/vehicle groups, are injected intraperitoneally with calcein nine days and two days before sacrifice (two injections of calcein administered each designated day, to ensure proper labeling of newly formed bone). Weekly body weights are determined. At the end of the 35-day cycle, the animals' blood and tissues are processed as described above.

Lead compounds may also be tested in chronic OVX animals (treatment model). An exemplary protocol for treatment of established bone loss in ovariectomized animals that can be used to assess efficacy of anabolic agents may be performed as follows. Briefly, 80 to 100 six month old female, Sprague-Dawley rats are subjected to sham surgery (sham OVX) or ovariectomy (OVX) at time 0, and 10 rats are sacrificed to serve as baseline controls. Body weights are recorded weekly during the experiment. After approximately 6 weeks (42 days) or more of bone depletion, 10 sham OVX and 10 OVX rats are randomly selected for sacrifice as depletion period controls. Of the remaining animals, 10 sham OVX and 10 OVX rats are used as placebo-treated controls. The remaining OVX animals are treated with 3 to 5 doses of test drug for a period of 5 weeks (35 days). As a positive control, a group of OVX rats can be treated with an agent such as PTH, a known anabolic agent in this model (Kimmel, et al., Endocrinology (1993) 132:1577-84). To determine effects on bone formation, the following procedure can be followed. The femurs, tibiae and lumbar vertebrae 1 to 4 are excised and collected. The proximal left and right tibiae are used for pQCT measurements, cancellous bone mineral density (BMD) (gravimetric determination), and histology, while the midshaft of each tibiae is subjected to cortical BMD or histology. The femurs are prepared for pQCT scanning of the midshaft prior to biomechanical testing. With respect to lumbar vertebrae (LV), LV2 are processed for BMD (pQCT may also be performed); LV3 are prepared for undecalcified bone histology; and LV4 are processed for mechanical testing.

Statin Compounds Useful in the Invention

The statin compounds useful in the methods and compositions of the invention are of the formula:

wherein X in each of formulas (1) and (2) represents a substituted or unsubstituted alkylene, alkenylene, or alkynylene linker of 2-6C;

Y represents one or more carbocyclic or heterocyclic rings; when Y comprises two or more rings, they may optionally be fused; and

R′ represents a cation, H or a substituted or unsubstituted alkyl group of 1-6C. It is understood that if R′ represents a cation with multiple positive charges, the appropriate number of anions is coupled with it. Formulas (1) and (2) are, respectively, the unhydrolyzed and hydrolyzed forms of the statin compounds. Preferred substituents on X (or on R′ when R′ is alkyl) are hydroxy, alkoxy, phenyl, amino and alkyl- or dialkylamino.

The compounds useful in the invention contain at least one and generally several chiral centers. Compounds useful in the invention include mixtures of the various stereoisomers and the stereoisomeric forms of the compounds individually. Preferred stereoisomers with respect to the compound of formula (1) are of the formula:

and the corresponding stereochemistry in the open chain (nonlactone or hydrolyzed) form of formula (2).

In one set of preferred embodiments, X is unsubstituted; most preferably X is selected from the group consisting of —CH₂CH₂—; —CH═CH—; and —C≡C—, especially —CH₂CH₂— and —CH═CH—.

Preferred embodiments of Y comprise ring systems such as naphthyl, polyhydro-naphthyl, monohydro- or dihydrophenyl, quinolyl, pyridyl, quinazolyl, pteridyl, pyrolyl, oxazoyl and the like and the reduced or partially reduced forms thereof.

Preferred embodiments of the substituent Y include those of the formula:

wherein the ring system may contain π-bonds;

wherein R¹ is substituted or unsubstituted alkyl;

each R² is independently a noninterfering substituent;

R³ is H, hydroxy, or alkoxy (1-6C);

each m is independently an integer of 0-6, wherein each R² may reside in any of positions 2-7; and

p is 0 or 1, depending on the position of any π-bonds.

Particularly preferred embodiments include those of formulas (4a)-(4f) wherein the upper limit of n is adjusted according to the valence requirements appropriate for the particular ring system.

While R¹ may be substituted alkyl, wherein the substituents may include hydroxy, alkoxy, alkylthiol, phenyl, phenylalkyl, and halo, unsubstituted alkyl is preferred. Particularly preferred embodiments of R¹ are alkyl of 1-6C, including propyl, sec-butyl, t-butyl, n-butyl, isobutyl, pentyl, isopentyl, 1-methylbutyl, and 2-methylbutyl. Particularly preferred are propyl and sec-butyl.

Preferred embodiments for R² include H, hydroxy, ═O, and substituted or unsubstituted lower alkyl (1-4C), in particular methyl, and hydroxymethyl. In the preferred embodiments, each n is independently 1 or 2 and preferred positions for substitution are positions 2 and 6 (see formula (4)). Particularly preferred embodiments of R² are OH, H, and lower alkyl, in particular CH₃.

Particularly preferred are embodiments wherein Y is 4(a) or 4(b), and especially embodiments having the substitution pattern indicated in formulas 4(g) and 4(h) below.

As indicated above, the compounds of the invention may be supplied as individual stereoisomers or as mixtures of stereoisomers. Preferred stereoisomers are those of the formulas (4g) and (4h) as typical and appropriate for those represented by the formulas (4a)-(4f).

Particularly preferred are compounds with the stereochemistry of formulas (4g) and (4h) wherein the noted substituents are the sole substituents on the polyhydronaphthyl system optionally including additional substituents at position 5. Preferred embodiments include those wherein each of R² is independently OH, CH₂OH, methyl, or ═O. Preferred embodiments of R¹ in these preferred forms are propyl, sec-butyl, and 2-methyl-but-2-yl.

Additional preferred embodiments of Y are:

wherein Z is N and both n are 1, and each K comprises a substituted or unsubstituted aromatic or nonaromatic carbocyclic or heterocyclic ring system which may optionally be spaced from the linkage position shown in formula (7) by a linker of 1-2C, including —CHOH—, —CO—, and —CHNH₂—, for example. Aromatic ring systems are preferred. Particularly preferred are compounds of formula (7), either as shown or wherein Z is contained in a 6-membered, rather than a 5-membered aromatic ring. Thus, another group of preferred compounds of the invention is of formula (7) where Z is N and an additional substituent —═CR⁶— is inserted between Z and the bond directed to X, wherein R⁶ is linear, branched or cyclic alkyl. In a preferred embodiment, R⁶ is a cyclic alkyl substituent.

R⁵ is H or linear, branched, cyclic substituted or unsubstituted alkyl, wherein substituents are preferably hydroxy, alkoxy, phenyl, amino and alkyl- or dialkylamino. Preferably, when R⁵ is alkyl, it is unsubstituted.

The substituents on the aromatic ring systems or nonaromatic ring systems of the invention including those designated by K can be any noninterfering substituents. Generally, the non-interfering substituents can be of wide variety. Among substituents that do not interfere with the beneficial effect of the compounds of the invention on bone formation in treated subjects include alkyl (1-6C, preferably lower alkyl 1-4C), including straight, branched or cyclic forms thereof, alkenyl (2-6C, preferably 2-4C), alkynyl (2-6C, preferably 2-4C), all of which can be straight or branched chains and may contain further substituents; halogens, including F, Cl, Br and I; silyloxy, OR, SR, NR₂, OOCR, COOR, NCOR, NCOOR, and benzoyl, CF₃, OCF₃, SCF₃, N(CF₃)₂, CN, SO, SO₂R and SO₃R wherein R is alkyl (1-6C) or is H. Where two substituents are in adjacent positions in the aromatic or nonaromatic system, they may form a ring. Further, rings not fused to the aromatic or nonaromatic system K may be included as substituents. These rings may be aromatic and may be substituted or unsubstituted.

Preferred non-interfering substituents include hydrocarbyl groups of 1-6C, including saturated and unsaturated, linear or branched hydrocarbyl as well as hydrocarbyl groups containing ring systems; halo groups, alkoxy, hydroxy, CN, CF₃, and COOR, amino, monoalkyl- and dialkylamino where the alkyl groups are 1-6C. Particularly preferred are substituted or unsubstituted aromatic rings.

Although the number of substituents on a ring symbolized by K may typically be 0-4 or 0-5 depending on the available positions, preferred embodiments include those wherein the number on a single ring is 0, 1 or 2, preferably 0 or 1. However, an exception is that of formula (8), where it is preferred that the aromatic carbocyclic or heterocyclic ring system be multiply substituted. In particular, it is preferred that the substituents on K in formula (8) themselves contain aromatic rings. Particularly preferred are substituents that contain phenyl rings.

Particularly preferred are the embodiments of formula (7) or the ring expanded form thereof wherein K represents optionally substituted phenyl. Particularly preferred are compounds wherein R⁵ is isopropyl and K is para fluorophenyl forms.

The compounds useful in the methods and compositions of the invention can be synthesized by art-known methods as they resemble a class of compounds known in the art to behave as antihypercholesterolemic agents. Typical among these is lovastatin, marketed by Merck as Mevacor®. The synthesis of lovastatin and various analogs thereof is set forth in U.S. Pat. No. 4,963,538, incorporated herein by reference. In addition, methods for synthesis of lovastatin and analogous compounds such as compactin (mevastatin), simvastatin, and pravastatin are set forth in U.S. Pat. Nos. 5,059,696; 4,873,345; 4,866,186; 4,894,466; 4,894,465; 4,855,456; and 5,393,893, all incorporated herein by reference. Certain of these compounds are also produced by microorganisms as described in U.S. Pat. Nos. 5,362,638; 5,409,820; 4,965,200; and 5,409,820, all also incorporated herein by reference. Compounds described as end-products in these documents are useful in the methods of the invention.

Additional analogs, including those containing aromatic embodiments of Y, are described in U.S. Pat. No. 5,316,765 incorporated herein by reference. For example, the preparation of fluvastatin is described in PCT Application WO84/02131. Other compounds are described in, for example, Roth, B. D., et al., J Med Chem (1991) 34:357-366; Krause, R., et al, J Drug Dev (1990) 3(Suppl. 1):255-257; Karanewsky, D. S., et al., J Med Chem (1990) 33:2952-2956.

Particularly preferred are hydrolyzed or unhydrolyzed forms of lovastatin (59-0326), mevastatin (59-0327), simvastatin (59-0328) fluvastatin (59-0342), pravastatin, cerivastatin, NK-104 and atorvastatin. Typical forms of these statins are shown in FIGS. 1A and 1B.

The compositions of the invention may also include the bisphosphonates and their analogs. Typically, and preferably, the bisphosphonates are of the formula

and the pharmaceutically acceptable salts, esters and amides thereof. Typical salts are those of the inorganic ions, such as sodium ion, potassium ion, calcium ion, magnesium ion and the like; any pharmaceutically acceptable cation may be used. Typical esters are the ethyl, methyl, isobutyl, ethylene glycol, and other typical pharmaceutically acceptable esters; typical amides are the unsubstituted —NH₂ amides as well as the alkyl and dialkyl amides.

Embodiments of R¹⁰ include halo, OR, SR, NR₂, where R is H or alkyl (1-6C) or alkyl or arylalkyl with optional substitutions. Particularly preferred are the amino-substituted alkyl embodiments. Typically, both R¹⁰ are not identical, although in some embodiments, such as clodronate, both R¹⁰ are halo. Particularly preferred compounds among the bisphosphonates are risedronate, alandronate, pamidronate, clodronate and in particular ibandronate. These compounds are particularly useful in combination with the statins.

In addition to the statins or other isoprenoid inhibiting compounds of the invention, the compositions may also include other agents, including those which inhibit bond resorption such as estrogens or their analogs and compounds of the formula Ar—L—Ar wherein Ar represents an aryl substituent and L represents a linker.

The following examples are intended to illustrate but not to limit the invention.

EXAMPLE 1 High Throughput Screening

Thousands of compounds have been tested in the assay system set forth in U.S. Ser. No. 08/458,434, filed Jun. 2, 1995, and incorporated herein by reference. Representative compounds of the invention gave positive responses, while the majority of (unrelated) compounds are inactive. In this screen, the standard positive control was the compound 59-0008 (also denoted “OS8”), which is of the formula:

In more detail, the 2T3-BMP-2-LUC cells, a stably transformed osteoblast cell line described in Ghosh-Choudhury, et al., Endocrinology (1996) 137:331-39, referenced above, was employed. The cells were cultured using α-MEM, 10% FCS with 1% penicillin/streptomycin and 1% glutamine (“plating medium”), and were split 1:5 once per week. For the assay, the cells were resuspended in a plating medium containing 4% FCS, plated in microtiter plates at a concentration of 5×10³ cells (in 50 μl)/well, and incubated for 24 hours at 37° C. in 5% CO₂. To initiate the assay, 50 μl of the test compound or the control in DMSO was added at 2× concentration to each well, so that the final volume was 100 μl. The final serum concentration was 2% FCS, and the final DMSO concentration was 1%. Compound 59-0008 (10 μM) was used as a positive control.

The treated cells were incubated for 24 hours at 37° C. and 5% CO₂. The medium was then removed, and the cells were rinsed three times with PBS. After removal of excess PBS, 25 μl of 1× cell culture lysing reagent (Promega #E153A) was added to each well and incubated for at least ten minutes. Optionally, the plates/samples could be frozen at this point. To each well was added 50 μl of luciferase substrate (Promega #E152A; 10 ml Promega luciferase assay buffer per 7 mg Promega luciferase assay substrate). Luminescence was measured on an automated 96-well luminometer, and was expressed as either picograms of luciferase activity per well or as picograms of luciferase activity per microgram of protein.

In this assay, compound 59-0008 (3-phenylazo-1H-4,1,2-benzothiadiazine) exhibits a pattern of reactivity which is maximal at a concentration of approximately 3-10 μM. Accordingly, other tested compounds can be evaluated at various concentrations, and the results compared to the results obtained for 59-0008 at 10 μM (which value would be normalized to 100). Alternatively, the reactivity of a compound to be tested can be compared directly to a negative control containing no compound.

A variety of statin compounds (simvastatin designated OS114 or 59-0328, hydrolyzed simvastatin, mevastatin designated 59-0327, lovastatin designated 59-0326, fluvastatin designated 59-0342, and pravastatin designated 59-0329) were tested in the in vitro BMP-promoter based (designated “ABA”) assay (as described at the beginning of this example above), and in some experiments were tested also in a control osteoblast/serum response element (OBSRE) cell-based assay and/or a control glucagon assay. In the negative control OBSRE assay, a murine osteoblast cell line, such as CCC-4 expressing a serum response element (SRE)-luciferase reporter gene is used (see WO96/07733). In the negative control glucagon assay, a glucagon receptor-positive BHK cell expressing a CRE-luciferase reporter gene is used (see U.S. Pat. No. 5,698,672).

The results of three separate determinations in the ABA assay are shown below. Most of the statins (i.e., simvastatin, hydrolyzed sinvastatin, mevastatin, lovastatin, and fluvastatin) exhibited a dose-dependent stimulatory effect in the ABA assay, but not in control assays. In one experiment, simvastatin demonstrated over a 20-fold induction in the ABA assay, as compared to the non-statin, ABA stimulatory compound 59-0008.

ABA Assay Results Sample Concentration Fold increase % 59-0008 over negative μM μg/ml Response control Experiment 1 Lovastatin 497 200 −22.650 −0.003 59-0326 248.5 100 −22.620 −0.001 124.25 50 −22.510 0.003 62.125 25 144.730 7.408 31.0625 12.5 153.790 7.809 15.5312 6.25 126.230 6.589 7.76562 3.125 111.730 5.947 3.88281 1.5625 67.080 3.970 1.94140 0.78125 35.220 2.559 0.97070 0.390625 27.830 2.232 0.48535 0.195312 22.840 2.011 Mevastatin 512 200 −1.600 0.929 59-0327 256 100 12.460 1.552 128 50 153.110 7.779 64 25 152.690 7.760 32 12.5 164.730 8.293 16 6.25 140.260 7.210 8 3.125 99.670 5.413 4 1.5625 47.630 3.103 2 0.78125 34.520 2.528 1 0.390625 15.650 1.693 0.5 0.195312 25.840 2.144 Simvastatin 477 200 −22.960 −0.009 59-0328 238.5 100 −23.010 −0.011 119.25 50 −22.950 −0.008 59.625 25 148.310 7.515 29.8125 12.5 131.300 6.768 14.9062 6.25 141.970 7.237 7.45312 3.125 135.610 6.957 3.72656 1.5625 99.170 5.356 1.86328 0.78125 69.600 4.057 0.93164 0.390625 38.210 2.679 0.46582 0.195312 29.030 2.275 Pravastatin 471 200 11.670 1.513 59-0329 235.5 100 7.620 1.335 117.75 50 5.000 1.220 58.875 25 3.520 1.155 29.4375 12.5 1.110 1.049 14.7187 6.25 0.920 1.040 7.35937 3.125 0.380 1.017 3.67968 1.5625 −1.120 0.951 0.83984 0.78125 −1.980 0.913 0.91992 0.390625 −1.290 0.943 0.45996 0.195312 −4.390 0.807 Fluvastatin 470 200 −22.700 −0.005 59-0342 235 100 −22.570 0.001 117.5 50 −22.660 −0.003 58.75 25 137.500 7.088 29.375 12.5 164.450 8.281 14.6875 6.25 165.630 8.333 7.34375 3.125 173.280 8.672 3.67187 1.5625 117.980 6.223 1.83593 0.78125 75.160 4.328 0.91796 0.390625 28.080 2.243 0.45898 0.195312 36.820 2.630 Hydrolyzed 477 200 −15.140 −0.0 simvastatin 238.5 100 −15.230 −0.0 119.25 50 44.520 3.9 59.625 25 200.230 14.3 29.8125 12.5 156.230 11.3 14.90625 6.25 150.260 10.9 7.453125 3.125 75.860 6.0 3.726562 1.5625 36.190 3.4 1.863281 0.78125 10.430 1.6 0.931640 0.390625 1.520 1.1 0.465820 0.195312 −0.680 0.9 Experiment 2 Mevastatin 100 39 88.860 6.9 59-0327 50 19.5 97.420 7.4 25 9.75 71.630 5.7 12.5 4.875 66.010 5.3 6.25 2.4375 36.210 3.4 3.125 1.21875 10.970 1.7 1.5625 0.609375 9.780 1.6 0.78125 0.304687 2.370 1.1 0.390625 0.152343 0.960 1.0 0.195312 0.076171 −0.090 0.9 0.097656 0.038085 2.880 1.1 Simvastatin 477 200 222.180 15.7 59-0328 238.5 100 304.100 21.2 119.25 50 189.430 13.5 59.625 25 180.640 13.0 29.8125 12.5 152.290 11.1 14.90625 6.25 104.640 7.9 7.453125 3.125 51.660 4.4 3.726562 1.5625 19.670 2.3 1.863281 0.78125 6.820 1.4 0.931640 0.390625 2.600 1.1 0.465820 0.195312 0.310 1.0 Experiment 3 Lovastatin 247 100 −32.660 −0.002 59-0326 77.1875 31.25 166.770 6.118 24.12109 9.765625 148.030 5.543 7.537841 3.051757 103.260 4.169 2.355575 0.953674 35.300 2.083 0.736117 0.298023 10.860 1.333 0.230036 0.093132 3.210 1.099 0.071886 0.029103 1.550 1.048 0.022464 0.009094 2.720 1.083 0.007020 0.002842 1.050 1.032 0.002193 8.88178E 0.620 1.019 Fluvastatin 235 100 60.3 4.14 59-0342 73.4375 31.25 122.53 7.38 22.94921 9.765625 103.7 6.4 7.171630 3.051757 22.66 2.18 2.241134 0.953674 2.3 1.12 0.700354 0.298023 −3.26 0.83 0.218860 0.093132 −2.11 0.89 0.068394 0.029103 −5.18 0.73 0.021373 0.009094 −3.84 0.8 0.006679 0.002842 −3.26 0.83 0.002087 8.88178E −0.19 0.99

The pravastatin that was tested did not exhibit a dose-dependent stimulatory response, but since this compound was extracted from formulated pravastatin, it is possible that insufficient and/or inactive compound was tested.

EXAMPLE 2 In vivo Calvarial Bone Growth Data

Lovastatin and simvastatin were assayed in vivo according to the procedure described previously (see “In vivo Assay of Effects of Compounds on Murine Calvarial Bone Growth,” supra). Simvastatin provided a 1.5 fold increase in the number of osteoblasts.

In one experiment, vehicle control, bFGF and varying doses of simvastatin (59-0328) and lovastatin (designated 59-0326) were tested in the in vivo calvarial bone growth assay. The results are reported as a measurement of total bone area (and % increase in area over vehicle control), as shown below.

Total Bone Compound Area (μm²) Control 167.7 bFGF (12.5 μg/kg/day) 242 (45%) 59-0328 10 mg/kg/day 245 (46%) 59-0328 5 mg/kg/day 202 (20%) 59-0328 1 mg/kg/day 172 (2%) 59-0326 10 mg/kg/day 239 (42%) 59-0326 5 mg/kg/day 235 (40%) 59-0326 1 mg/kg/day 237 (41%) 59-0326 0.1 mg/kg/day 162 (0%)

Both simvastatin and lovastatin stimulated a dose-dependent increase in total bone area. At 10 mg/kg/day, the bone stimulatory effects of these statins were comparable to the bone growth effect observed when 12.5 μg/kg/day bFGF was tested in the same assay.

EXAMPLE 3 In vitro Bone Formation

Selected compounds and appropriate controls were assayed in vitro (ex vivo) for bone formation activity (described above in “Neonatal Mouse Calvaria Assay (in vitro)”). Histomorphometrical assessments of ex vivo calvaria were carried out using an OsteoMetrics bone morphometry measurement program, according to the manufacturer's instructions. Measurements were determined using either a 10- or 20-fold objective with a standard point counting eyepiece graticule.

New bone formation was determined (using a 10× objective) by measuring the new bone area formed in one field in 3 representative sections of each bone (4 bones per group). Each measurement was carried out ½ field distance from the end of the suture. Both total bone and old bone area were measured. Data were expressed as new bone area in mm².

Osteoblast numbers were determined by point counting. The number of osteoblast cells lining the bone surface on both sides of the bone were counted in one field using a 20× objective. Data were expressed as osteoblast numbers/mm of bone surface.

Lovastatin and simvastatin and control compounds/factors bFGF and BMP-2, and a vehicle control were tested in the in vitro bone formation assay and the calvaria were analyzed histomorphometrically, as described above. Several sets of experimental data are presented below, with % increase over vehicle control values indicated parenthetically.

Osteoblast Number: 3 days 7 days Compound Obs/field Obs/field Experiment 1 Control 97.25 92.7 59-0328 156 (63%) 154 (68%) BFGF 179.25 (84%) 168.7 (82%) BMP-2 127 (31%) 119 (28%) Experiment 2 Control 90.7 59-0328 154 (70%) Experiment 3 Control 84 59-326 128 (152%)

New Bone Area: 3 days 7 days Compound (mm² × 10⁻³) (mm² × 10⁻³) Experiment 1 Control 4.8 7.8 59-0328 8.5 (77%) 17.4 (123%) BFGF 5.7 (19%) 18.1 (132%) BMP-2 8.4 (75%) 18.7 (140%) Experiment 2 control 4.0 59-0328 15.4 (285%) Experiment 3 Control 4.5 590-326 8.2 (182%)

These data show that lovastatin and simvastatin are as good as, or better than, BMP-2 and bFGF (two “gold standard” agents for bone growth; see Wozney J., Molec Reprod Dev (1992) 32:160-67; WO95/24211) for inducing bone formation. As shown in Example 2, in vivo calvarial studies using lovastatin and simvastatin have provided bone growth data consistent with these in vitro observations.

EXAMPLE 4 Effect on Resorption

The statins and controls were tested in an antiresorptive assay. Briefly, 15 day timed pregnant CD-1 female mice were injected with ⁴⁵Ca (25 μCi/mouse). The calvaria from the 4 day old pups were dissected out and cut in half. The excised half calvaria were placed on metal grids (at the surface) in 1 ml of BGJ medium (Sigma) containing 0.1% BSA with glutamine and Pen/Strep added. The bones were incubated at 37° C. in a 5% humidified incubator for a period of 24 h, and then were transferred to wells containing 1 ml medium with factors added (IL-1, PTH, and/or test compounds). The treated bones were incubated under the above conditions for a further 72 h. After this incubation period, the bones were removed and placed into 20% TCA in a scintillation vial for 1.5 h, and then counted with scintillation fluid. An aliquot of medium (0.4 ml) was also counted. The results were expressed as % ⁴⁵Ca release.

This assay may be modified by including test compounds/factors or control compounds/factors in the preincubation medium (i.e., during the first 24 h). Since most of the osteoclasts are formed in the calvaria following the preincubation period, compounds or factors that affect osteoclast formation may have a greater effect during the preincubation period.

In this assay, compound toxicity was indicated by obvious death of the cells in the periosteal region and within the marrow cavity of the bone organ cultures. These cells were characterized by pyknotic nuclei and vacuolated cytoplasm, characteristic of cell necrosis and distinct from apoptosis.

Using this assay, simvastatin was tested for its ability to inhibit IL-1 induced bone resorption. Briefly, IL-1 (10⁻¹⁰M) was added simultaneously with simvastatin (at 0.1, 1 or 10 μM) during a 72 h incubation period. Bone resorption was determined by measuring ⁴⁵Ca release. IL-1, in the absence of simvastatin, increased ⁴⁵Ca release about 2-fold over control calvaria incubated in the absence of IL-1 or simvastatin. Simvastatin at 0.1 or 1 μM concentration did not alter IL-1 induced ⁴⁵Ca release. However, simvastatin at 10 μM concentration decreased IL-1 induced ⁴⁵Ca release.

Histologic evaluation indicated toxicity at the 10 μM simvastatin. Previous studies have correlated toxicity with decreased ⁴⁵Ca release.

These data suggest that simvastatin does not inhibit bone resorption at doses effective in the primary screening assay of Example 1. These results are contrary to reports by R. G. G. Russell and colleagues that mevastatin inhibits bone resorption in murine calvariae in vitro.

EXAMPLE 5 Systemic Administration of Statins in OVX Models

Lovastatin and simvastatin were analyzed in vivo using an acute OVX (prevention model) and/or chronic (treatment model) OVX model system, as described above under “Additional In Vivo Assays”.

Lovastatin was examined in an acute OVX study. Briefly, 59-0326 was orally administered (35, 7, or 1.4 mg/kg/day; once per day for 35 days) immediately following ovariectomy. At the end of the study, the animals' blood and tissues samples were processed, and the following data were obtained.

pQCT analysis of samples removed from animals that received the 7 mg/kg/day dose showed a 20% increase in trabecular density and a 14% increase in cortical thickness. Histomorphometric analysis by two individuals showed an increase in trabecular bone volume of 110% (p<0.001) or 25% (p=0.0503) in the proximal tibia, and an increase of 23% (not significant) in the distal femur. The bone formation rate in the distal femur was increased 40% (p=0.052) in the 7 mg/kg/day animals.

Similarly, lovastatin was orally administered (0.1, 1, 5, 10, 20 or 40 mg/kg/day; once per day for 35 days) immediately following ovariectomy. Two individuals histomorphometrically analyzed samples removed from animals that received the 10 mg/kg/day dose. These analyses indicated an increase in trabecular bone volume of 38% (not significant) or 90% (p<0.02) in the proximal tibia. The bone formation rate in the proximal tibia was determined to have increased 74% (p=0.004) in animals that received a 10 mg/kg/day dose or 37% (p<0.008) in animals that received a 1 mg/kg/day dose. In samples from animals that received the 1 mg/kg/day dose, mineral apposition rate in the proximal tibia was increased 22%.

Simvastatin was also examined in a chronic OVX study. Briefly, simvastatin was orally administered (0.1, 1, 10, or 50 mg/kg/day; once per day for 10 weeks) to rats at 6 weeks post-ovariectomy. At the 10 mg/kg/day dose, a 114% (not significant) increase in the bone formation rate in the proximal tibia was measured. At the 50 mg/kg/day dose, an 86% (not significant) increase in the bone formation rate in the proximal tibia was measured.

EXAMPLE 6 Statin-Mediated Fracture Repair Effects of Test Compounds

Simvastatin was examined for effects on surgical defects in the rabbit radius. Healing of these defects may be assessed by X-ray, histology and biomechanical strength.

The test compound was weighed out in a microcentrifuge tube, and 50 μl of 1.5% sodium alginate solution was added as a carrier. This test sample was vortexed to wet all of the powder. The sample was sonicated for 20-30 min, and then vortexed again. Disks were created in the top of the microcentrifuge tube (by placing the tube lid or stopper-side down). The indent in the top of the stopper (i.e., lid) was used to form the disk (7.5 mm diameter). CaCl₂ solution (100 μl of 100 mM) was added to the sodium alginate/drug solution. The samples were allowed to sit for 5-10 min, and then the calcium-alginate disks were carefully removed. The disks were rinsed in a beaker filled with water to rinse off the excess calcium solution, and were saved in tubes using water as vehicle. All solutions and containers were sterile, and all procedures for preparations of disks were performed under a laminar flow hood under sterile conditions.

Bone healing was examined as follows. Briefly, six-month old male rabbits were obtained, and were divided into 4 treatment groups (n=3 animals/group). The treatment groups received either: 1) placebo; 2) test compound (5 mg/disk); 3) test compound (10 mg/disk); or 4) an autologous bone graft. Animals were anesthetized with rabbit cocktail (1 ml/1.5 kg intramuscularly), and the right forelimb was clipped, prepped and draped for aseptic surgery. Anesthesia was maintained using isofluorane delivered with a face mask. To create a 20 mm gap defect in the right mid-radius, an incision was made over the lateral aspect of the forearm, and an osteotomy was performed with an oscillating bone saw. The simvastatin or vehicle was applied to the defect and the defect was closed in layers. No external splinting was needed, as the radius is paired with the ulna, which functions to allow normal ambulation in the rabbit. Disks were cut on strips and inserted in the fracture to cover all the defect. Radiologic evaluation was performed at zero time and at 4 weeks.

Because the vehicle (placebo treatment group) prevented full healing in the control group, only X-ray results were obtained and analyzed. Accordingly, X-ray analysis 4 weeks after initiation of treatment showed callus formation at the bone treatment site in the treated (both doses), but not the placebo (vehicle or autologous bone graft) groups.

EXAMPLE 7 Effect of Ras Inhibition on Bone Formation

The 2T3 osteoblast progenitor cell line, described by Ghosh-Choudhury, et al., Endo (1995) 137:331-339 is BMP-2 responsive and undergoes bone formation spontaneously in culture in vitro. These cells were stably transfected with the human dominant negative H-ras (Dn-ras) cDNA; this negative mutant gene contains an asparagine substitution at position 17 and production of this protein effects inhibition of endogenous ras. The Dn-ras coding sequence was under transcriptional control of the dexamethasone inducible mouse mammary tumor virus promoter. The production of the negative ras protein was confirmed by Western blot.

The cells were cultured on 24-well plates at a density of 2×10⁴/well and cultured with αMEM medium supplemented with 10% SDS for nodule formation assay indicating bone growth. Bone cell differentiation and module formation were monitored using a mineralized module formation assay described by Bharagava, et al., Bone (1986) 8:155-163 using van Kossa stain. The cultures were washed with phosphate buffered formalin, then with water and dehydrated in 70%, 95% and 100% ethanol, 2× each and then air-dried. The plates were rehydrated before staining; the water was removed, a 2% silver nitrate solution was added and the plates were exposed to sunlight for 20 minutes. The plates were rinsed with water and 5% sodium thiosulfate was added for 3 minutes and then rinsed. Modified van Gleson stain was used as a counterstain for unmineralized collagen matrix. Acid fuschin solution was added for 5 minutes and the plates were then washed and dried for image analysis.

The area of van Kossa stained nodules was quantified by an automated image analysis using a video analysis program (Jandel Scientific, San Raphael, Calif.) linked to a video screen camera equipped with metallurgical lenses. The nodule structures were also analyzed by transmission electron microscopy.

When the cells containing the Dn-ras gene were activated by incubation with 10⁻⁷ M dexamethasone, a dramatic and spontaneous formation of mineralized bone nodules resulted. This result did not occur in wild-type cells in the absence of added BMP. Thus, inhibition of ras function causes osteoblasts to differentiate and form bone.

EXAMPLE 8 Stimulation of In Vitro Calvarial Bone Formation by Bisphosphonates

Various bisphosphonates were tested for their ability to stimulate calvarial bone formation in vitro in the assay described in Example 3 both alone and in combination with 59-0328 (simvastatin). The results were calculated as new bone area in mm²×10⁻³, as above.

Dose response curves for ibandronate as a typical bisphosphonate showed a significant increase of bone formation at 10 μM ibandronate. These results are summarized below:

New Bone Area (mm² × 10⁻³) Experiment 1 Experiment 2 Experiment 3 Control 3.4 ± 0.5 3.5 ± 0.45 4.8 ± 0.6 0.01 μM — 3.5 ± 0.43 — 0.1 μM — 3.2 ± 0.56 6.2 ± 0.6 1 μM — 4.9 ± 1.2 7.5 ± 0.7 10 μM 8.3 ± 0.7 7.2 ± 0.7 9.5 ± 2.4 100 μM Toxic Toxic Toxic 1000 μM Toxic Toxic —

Other bisphosphonates were tested as shown below; although alendronate, pamidronate and clodronate gave negligible effects under these conditions, risedronate showed significant increases in new bone area at 10 μM and 100 μM concentrations.

New Bone Area (mm² × 10⁻³) Alendronate Pamidronate Clodronate Risedronate Control 3.8 ± 0.5 5.0 ± 0.2 3.9 ± 0.5 3.8 ± 0.4 0.1 μM 3.5 ± 0.3 — — — 1 μM 5.2 ± 0.5 — — — 10 μM 3.3 ± 0.6 6.0 ± 0.5 4.8 ± 1.3 8.5 ± 0.5 100 μM Toxic 5.8 ± 0.6 4.6 ± 0.6 7.3 ± 1.9 1000 μM — 5.2 ± 0.6 3.5 ± 0.5 Toxic

The effect of ibandronate together with simvastatin was also tested. The results are shown as follows:

New Bone Area (mm² × 10⁻³) IBN (10 μM) IBN (1 μM) Control  4.13 ± 0.035 3.77 ± 0.93 Ibandronate (IBN) 6.03 ± 1.56 3.95 ± 0.28 59-0328 (0.2 μM) 6.83 ± 1.54 5.23 ± 0.89 59-0328 (0.1 μM) 4.25 ± 0.59  5.1 ± 0.49 IBN + 328 (0.2 μM) 12.1 ± 1.7   7.6 ± 0.61 IBN + 328 (0.1 μM) 8.15 ± 0.77 7.82 ± 1.31

As shown, the combination of 59-0328 with ibandronate was superior to the result with either bisphosphonate alone.

From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims. 

What is claimed is:
 1. A method to identify a compound for treating bone disorders in vertebrates which method comprises contacting said compound with an assay mixture for the activity of an enzyme in the isoprenoid pathway; determining the activity of the enzyme in the presence as compared to the absence of said compound; wherein a decrease of activity of said enzyme in the presence as opposed to the absence of said compound indicates that the compound will be useful in treating bone disorders in vertebrates.
 2. The method of claim 1 wherein the enzyme is a prenylation enzyme.
 3. The method of claim 1 wherein the enzyme is HMG-CoA reductase.
 4. The method of claim 1 wherein the enzyme participates in the conversion of mevalonic acid to transgeranyl pyrophosphate.
 5. The method of claim 1 wherein the enzyme converts transgeranyl pyrophosphate to transfarnesyl pyrophosphate. 